Platinum alloy electrodeposition bath and process for manufacturing platinum alloy electrodeposited product using the same

ABSTRACT

This invention provides a platinum alloy electrodeposition bath which, by alloying platinum with other metals, enables thick plating and can give platinum alloy layers having superior luster and hardness, and also provides a process for manufacturing a platinum alloy electrodeposited product using the same. 
     The platinum alloy electrodeposition bath according to this invention contains 2 to 100 g/lit. of platinum in the form of Pt(OH) 6   2-  complex ion and at least one of Sn, Zn and Pd in an amount of 1 mg/lit or more.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrodeposition bath of platinum alloywhich has characteristics superior to that of pure platinum in terms ofluster and high hardness and allows thick plating and to a process formanufacturing a platinum alloy electrodeposited product using the same.

2. Description of the Prior Art

Platinum is widely used as a noble metal material for decoration. Suchdecorative platinum are obtained using a known platinum plating bath,for example, as disclosed in Japanese Laid-Open Patent Publication No.Hei-2-107794.

However, such conventional platinum plating baths have problems in thatthey give deposits with lusterless appearance or low hardness, cannotachieve thick plating or has inconsistent deposition efficiency, andthus they are not very preferable for decoration. In addition,industrial use of such platinum plating has been limited to the fieldssuch as electrodes manufacturing.

SUMMARY OF THE INVENTION

The present invention is to provide a platinum alloy electrodepositionbath employing no pure platinum but an alloy of platinum and othermetals, whereby allowing thick plating, giving lustrous or high-hardnessplatinum alloy layers, and a process for manufacturing a platinum alloyelectrodeposited product using the same.

In the preceding and following descriptions, the term"electrodeposition" is used as having a broad concept which includeselectroplating and electro forming.

These and other objects of the invention will become more apparent upona reading of the following detailed description and embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to achieve the above-mentioned objects, the platinum alloyelectrodeposition bath according to this invention contains 2 to 100g/lit. of platinum in the form of Pt(OH)₆ ²⁻ complex ion and at leastone of Sn, Zn and Pd in an amount of 1 mg/lit. or more.

In this case, Sn assumes a stable,state in the form of Sn(OH)₆ ²⁻ andallows to give excellent platinum-tin alloy layers.

Further, Zn assumes a stable state if it is present in the bath in theform of Zn(OH)₃ ⁻ or Zn(OH)₄ ²⁻ and allows to give excellentplatinum-zinc alloy layers.

Pd may be present in the electrodeposition bath in the form of [Pd(NH₃)₂]²⁺ , [Pd(NH₃)₂ X₄ ]²⁻ or [Pd(NH₃)₄ ]²⁺, wherein X is a monovalentanion. Pd is stable when it is present in the bath in the form ofcomplexion expressed by [Pd(NH₃)n]²⁺, wherein n is 1 to 4. In this case,a halogen anion such as I⁻, B⁻, Cl⁻ and F⁻ may further be coordinated.Meanwhile, stability of Pd can further be increased by allowingamidosulfuric acid (sulfamic acid), potassium amidosulfate (potassiumsulfamate) or sodium amidosulfate (sodium sulfamate) to be present inthe electrodeposition bath.

If Pd is reacted with an oxidizing agent such as sodium peroxodisulfateand potassium peroxodisulfate prior to its addition to theelectrodeposition bath, it can be present in the bath in a more stablestate. Move stable complex ion can again be obtained by reacting it witha halogen ion in addition to NH₃.

Subsequent reactions may proceed beneficially if Pd is used in the formof salt such as Pd(NH₃)₄ Cl₂, Pd(NH₃)₂ Cl₂ and Pd(NH₃)₄ (OH)₂. Additionof a carboxylic acid such as citric acid, oxalic acid, acetic acid,malic acid and tartaric acid or alkali metal salts of carboxylic acidsto the bath effectively served to improve uniformity in the appearanceof the deposits, to prevent cracking or to stabilize the bath.

Although not so conspicuous as in the ease of carboxylic acids, additionof an alkali metal salt of sulfuric acid or phosphoric acid broughtabout the same effects.

Referring to operational conditions, while DC power supply can of coursebe employed, a pulse power supply may be used to vary the electrodepositcomposition and to make the metal layer appearance smooth.

The pH of the bath is preferably 11 or higher, and more preferably 12.5or higher. The bath temperature is preferably 60° C. or higher, and morepreferably 80° C. or higher.

The hardness of the electrodeposit may sometimes be increased byrecrystallization, if it is subjected to heat treatment as apost-treatment.

It is also possible to melt the ground metal and use the resulting metallayer as a film.

The platinum alloy electrodeposition bath and the process formanufacturing a platinum alloy electrodeposited product using the sameaccording to tile present invention is as described above. Thus, notonly the cost of ground metal can be reduced by using the platinumalloy, but also luster and high hardness, which are the propertiesunattainable by use of a pure platinum plating bath or pure platinumelectroforming bath, can be imparted to the deposit film.

The followings are descriptions of preferable embodiments according tothe present invention.

    ______________________________________                                        First Embodiment:                                                             ______________________________________                                        (1) Electrodeposition bath composition                                            K.sub.2 Pt(OH).sub.6 10 g/lit. (in terms of Pt)                               ZnO alkaline solution                                                                              0.2 g/lit. (in terms of Zn)                              KOH                  60 g/lit.                                            (2) Operational condition                                                         Current density      1 A/dm.sup.2                                             Temperature          90° C.                                            Electrodeposition time                                                                             120 min.                                             (3) Result                                                                    ______________________________________                                    

A lustrous product with approximate 17-μm thickness of platinum zincalloy was obtained. The Pt purity of the lustrous product was 96%.

    ______________________________________                                        Second Embodiment:                                                            ______________________________________                                        (1) Electrodeposition bath composition                                            K.sub.2 Pt(OH).sub.6 10 g/lit. (in terms of Pt)                               K.sub.2 SnO.sub.3.3H.sub.2 O solution                                                              15 g/lit. (in terms of Sn)                               KOH                  20 g/lit.                                            (2) Operational condition                                                         Current density      2 A/dm.sup.2                                             Temperature          90° C.                                            Electrodeposition time                                                                             240 min.                                             (3) Result                                                                    ______________________________________                                    

A semilustrous product of platinum-tin alloy with approximate 30-μmthickness was obtained. The Vickers hardness was found to be 600 to 850Hv. The Pt purity of the semi lustrous product was 85%.

    ______________________________________                                        Third Embodiment:                                                             ______________________________________                                        (1) Electrodeposition bath composition                                            K.sub.2 Pt(OH).sub.6 20 g/lit. (in terms of Pt)                               Pd(NH.sub.3).sub.4 (OH).sub.2                                                                      0.3 g/lit. (in terms of Pt)                              KOH                  30 g/lit.                                            (2) Operational condition                                                         Current density      3 A/dm.sup.2                                             Temperature          90° C.                                            Electrodeposition time                                                                             120 min.                                             (3) Result                                                                    ______________________________________                                    

A nonlustrous product platinum-palladium alloy layer with approximate50-μm thickness was obtained. After the ground metal was melted, thedeposit film was subjected to heat treatment at 350° C. for 2 hours inN₂ atmosphere. Thus, a flexible foil of Pt/Pd alloy was obtained. The Ptpurity of the foil was 90%.

What is claimed is:
 1. A platinum alloy electrodeposition bathcomprising 2 to 100 g/lit. of platinum in tile form of Pt(OH)₆ ²⁻complex ion and at least one ion of Sn, Zn and Pd in an amount of 1mg/lit or more.
 2. The platinum alloy electrodeposition bath accordingto claim 1, wherein the at least one ion of Sn, Zn and Pd is present inan amount of 50 mg/lit. to 100 g/lit.
 3. The platinum alloyelectrodeposition bath according to claim 1, wherein the Sn ion ispresent in the form of sodium stannate or potassium stannate.
 4. Theplatinum alloy electrodeposition bath according to claim 1, wherein theSn ion is present in the form of Sn(OH)₆ ²⁻.
 5. The platinum alloyelectrodeposition bath according to claim 1, wherein the Zn ion ispresent in the form of zinc oxide.
 6. The platinum alloyelectrodeposition bath according to claim 1, wherein the Zn ion ispresent in the form of Zn(OH)₃ ⁻ or Zn(OH)₄ ²⁻.
 7. The platinum alloyelectrodeposition bath according to claim 1, wherein the Pd ion ispresent in the form of Pd(NH₃)₄ Cl₂, Pd(NH₃)₂ Cl₂ or Pd(NH₃)₄ (OH)₂. 8.The platinum alloy electrodeposition bath according to claim 1, whereinthe Pd ion is present in the form or [Pd(NH₃)₂ ]²⁺, [Pd(NH₃)₂ X₄ ]²⁻ or[Pd(NH₃)₄ ]²⁺ (wherein X is a monovalent anion).
 9. The platinum alloyelectrodeposition bath according to claim 8, wherein the bath furthercontains at least one or amidosulfuric acid, sodium amidosulfate andpotassium amidosulfate.
 10. The platinum alloy electrodeposition bathaccording to claim 1, wherein the bath further contains a carboxylicacid or a carboxylic acid alkali metal salt.
 11. The platinum allowelectrodeposition bath according to claim 1 wherein Pd is present in theform of [Pd(NH₃)_(n) ]²⁺ (wherein n is equal to 2 or 4).
 12. In aprocess for manufacturing a platinum alloy product by electrodepositingplatinum alloys upon the surface of an object, the improvement whichcomprises using an electrodeposition bath comprising 2 to 100 g/lit. ofplatinum in the form of Pt(OH)₆ ²⁻ complex ion and at least one of Sn,Zn and Pd in an amount of 1 mg/lit. or more.
 13. An electrodepositionprocess according to claim 12 wherein, during the process, the pH of thebath is 11 or higher and the bath temperature is 60° C. or higher. 14.An electrodeposition process according to claim 12 wherein the processis carried out using a pulse power source as the source of electricalcurrent for such process.